RFID tags are used in a multitude of situations and may need to operate in two or more distinct conditions or states. A basic example of when an RFID tag is configured to alternate between two different states is when an RFID tag can be activated and deactivated. For example, RFID tags may be deactivated by disrupting the radio frequency (RF) field of the tag.
U.S. patent application Ser. No. 12/477,064, listing a common inventor and assignee to the present application, describes a number of designs for creating a two-state RFID tag. In that disclosure, an RFID tag is deactivated, not by blocking the field or by use of a mechanical switch (two common arrangements), but rather by capacitively shorting sections of the RFID tag, such that the tag would not absorb RF energy.
A further example of such an on/off, two state tag is illustrated in FIGS. 2A-2B. As shown the tag 200 includes a housing 202 and a slidable panel 204. An RFID inlay 206 is printed on a surface of the housing, and an RFID shorting structure 208 is disposed on the slidable panel.
In FIG. 2A, the panel 204 is positioned in a first position, such that the RFID shorting structure 208 and the RFID inlay 206 are aligned. This causes a capacitive electrical connection between the RFID shorting structure and the inlay. As such, sections of the inlay 206, in particular antenna sections, are shorted such that that the inlay's antenna would not absorb RF energy. In FIG. 2B, the panel 204 is moved to a second position, such that the RFID shorting structure 208 is moved out of alignment with the RFID inlay. This therefore allows the RFID inlay 206 to absorb RF energy, and accordingly respond to received RFID read requests.
Although the '064 application, and the above-described design of FIGS. 2A-2B, describe tags that have a number of advantages over other solutions for creating a switching tag, these tags nevertheless do have disadvantages. For example, that application does not disclose any type of arrangement that may provide for more than two states in a tag, or providing for two states in a tag that are recognizable at a reader due to received responses. This is because, in the deactivated state, the tag is essentially transparent to an RFID reader.